"Exactly why a proportion of the devices had the spontaneous reboot issue when not all do is a very good question. Interestingly, there was no report of this from the 300 preprodnuction"

well its more likely to be a slightly different component (probally diferent brand)- that has caused the rebooting- the problem is the driver that controls it not allowing for the tollerance in this probally only very slightly different component, the devices that reboot are later ones i think, not early ones.